The present invention relates to a method for use in network acquisition, and to a related cellular radio communication device.
The dead time that arises between the turning on of a cellular phone and network acquisition has for sometime been the subject of review and research in an attempt to limit the extent of such wasted time and its associated problems. For example, it has been noted that such dead time is a cause of irritation to the user, and the longer the time taken to achieve network acquisition subsequent to turning on the cellular device, the greater the irritation caused.
Also, the network acquisition procedure conducted during this period is one that requires a significant amount of power to be expended within the hand set. Thus as handsets move to dual mode or multimode functionality, the potential for such aforementioned irritation and power expense is likely to increase yet further. Within dual mode or multimode handsets, there are of course a plurality of sets of frequencies to search and so connecting to the most attractive cell on the best network will take proportionately longer and the power consumed will be correspondingly proportionately higher.
Also, certain specifications arising in accordance with mobile network standards also place constraints upon the operation of a mobile handset within a cellular network, which can also have disadvantageous effect on the above-mentioned dead time. For example, under 3GPP (3rd Generation Partnership Project) specifications, a handset is required to search one entire radio access technology (RAT) at a time. The relative priority of RATs is set within the handset and so, for example, a dual mode GSM (Global System for Mobile Communication)/UMTS (Universal Mobile Telecommunication System) handset will first search either on the GSM or UMTS radio technology, and will only look at the second RAT during initial selection if no suitable cells are found on the first RAT.
While improvements in the initial search procedures have been made in an attempt to reduce the dead time experienced by the user and/or to reduce the handset energy consumption, further advances in improving the efficiency of network acquisition are still desired.
In some handsets a procedure is provided whereby, before starting a scan of a network, the handset is arranged to look for the base station that it was last attached to before the handset was turned off. Thus, on subsequent turn on at the handset, if the handset has not changed location, the handset can camp on the cell relatively rapidly in view of the information retained concerning the base station previously attached to. A handset arranged to operate in such a known cell mode can then camp on the cell within a period in the region of 1 second, as compared with periods of up to 30 seconds when conducting a full cell search.
Such known cell operation is disadvantageously limited since its successful operation is dependent very much upon the user turning off their handset, and subsequently turning on a handset, at the same location and this will rarely hold true.